refactor(examples): use slot render helpers

Use the slhx RenderSlotExt path for board updates so examples no longer manually compose SafeHtml before slot replacement.

req: dx/006

req: component/003

examples/techdemo/src/main.rs

@@ -415,7 +415,7 @@ fn update_work(demo: &mut DemoState, id: Option<&str>, update: impl FnOnce(&mut
 fn demo_effects(demo: &DemoState, notice: &'static str) -> impl IntoEffect {
     (
         slots::hero_metrics.render(&hero_view(demo)),
-        slots::board.html(ui::render(&board_view(demo))),
+        slots::board.render(&board_view(demo)),
         slots::activity.render(&activity_view(demo)),
         slots::inspector.render(&inspector_view(demo)),
         slots::notice.text(notice),